Fair Value Measurements (Summary Of Estimated Fair Value Of Derivative Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value of derivative financial instruments	$ 176,956	$ 173,236
Oil And Natural Gas Derivative Financial Instruments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value of derivative financial instruments	176,956	173,236
Oil And Natural Gas Derivative Financial Instruments [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value of derivative financial instruments
Oil And Natural Gas Derivative Financial Instruments [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value of derivative financial instruments	176,956	173,236
Oil And Natural Gas Derivative Financial Instruments [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value of derivative financial instruments